[PATCH v1 09/11] x86: perf: intel_pt: Add core dump functionality

Alexander Shishkin
2014-02-06T10:52:37Z

Intel Processor Trace (PT) data can be used in process core dumps. This
is done by implementing itrace code dump related hooks that configure and
output trace data to a core file. The driver will also include the list
of PT capabilities in itrace core dump notes so that the decoder can make
assumptions about the binary stream.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
---
arch/x86/kernel/cpu/intel_pt.h | 2 +
arch/x86/kernel/cpu/perf_event_intel_pt.c | 74 +++++++++++++++++++++++++++++++
2 files changed, 76 insertions(+)

diff --git a/arch/x86/kernel/cpu/intel_pt.h b/arch/x86/kernel/cpu/intel_pt.h
index dd69092..befde1f 100644
--- a/arch/x86/kernel/cpu/intel_pt.h
+++ b/arch/x86/kernel/cpu/intel_pt.h
@@ -84,6 +84,8 @@ enum pt_capabilities {
struct pt_pmu {
struct itrace_pmu itrace;
u32 caps[4 * PT_CPUID_LEAVES];
+ char *capstr;
+ unsigned int caplen;
};

/**
diff --git a/arch/x86/kernel/cpu/perf_event_intel_pt.c b/arch/x86/kernel/cpu/perf_event_intel_pt.c
index af1482d..cb03594 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_pt.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_pt.c
@@ -24,6 +24,7 @@
#include <linux/slab.h>
#include <linux/debugfs.h>
#include <linux/device.h>
+#include <linux/coredump.h>

#include <asm-generic/sizes.h>
#include <asm/perf_event.h>
@@ -88,6 +89,34 @@ static void pt_cap_set(enum pt_capabilities cap, u32 val)
pt_pmu.caps[idx] = (val << shift) & cd->mask;
}

+/**
+ * pt_cap_string - format PT capabilities into an ascii string
+ *
+ * We need to include PT capabilities in the core dump note so that the
+ * decoder knows what to expect in the binary stream.
+ */
+static void pt_cap_string(void)
+{
+ char *capstr;
+ int pos, i;
+
+ capstr = kzalloc(PAGE_SIZE, GFP_KERNEL);
+ if (!capstr)
+ return;
+
+ for (i = 0, pos = 0; i < ARRAY_SIZE(pt_caps) && pos < PAGE_SIZE; i++) {
+ pos += snprintf(&capstr[pos], PAGE_SIZE - pos, "%s:%x%c",
+ pt_caps[i].name, pt_cap_get(i),
+ i == ARRAY_SIZE(pt_caps) - 1 ? 0 : ',');
+ }
+
+ if (pt_pmu.capstr)
+ kfree(pt_pmu.capstr);
+
+ pt_pmu.capstr = capstr;
+ pt_pmu.caplen = pos;
+}
+
static ssize_t pt_cap_show(struct device *cdev,
struct device_attribute *attr,
char *buf)
@@ -114,6 +143,7 @@ static ssize_t pt_cap_store(struct device *cdev,
return -EINVAL;

pt_cap_set(cap, new);
+ pt_cap_string();
return size;
}

@@ -179,6 +209,7 @@ static int __init pt_pmu_hw_init(void)
attrs[i] = &de_attrs[i].attr.attr;
}

+ pt_cap_string();
pt_cap_group.attrs = attrs;
return 0;

@@ -1070,6 +1101,46 @@ out:
pt_event_start(event, 0);
}

+static size_t pt_trace_core_size(struct perf_event *event)
+{
+ return pt_pmu.caplen;
+}
+
+static unsigned int pt_core_copy(void *data, const void *src,
+ unsigned int len)
+{
+ struct coredump_params *cprm = data;
+
+ if (dump_emit(cprm, src, len))
+ return 0;
+
+ return len;
+}
+
+static void pt_trace_core_output(struct coredump_params *cprm,
+ struct perf_event *event,
+ unsigned long len)
+{
+ struct pt_buffer *buf;
+ u64 from, to;
+ int ret;
+
+ buf = itrace_priv(event);
+
+ if (!dump_emit(cprm, pt_pmu.capstr, pt_pmu.caplen))
+ return;
+
+ to = local64_read(&buf->head);
+ if (to < len)
+ from = buf->size + to - len;
+ else
+ from = to - len;
+
+ ret = pt_buffer_output(buf, from, to, pt_core_copy, cprm);
+ if (ret < 0)
+ pr_warn("%s: failed to copy trace data\n", __func__);
+}
+
static __init int pt_init(void)
{
int ret, cpu;
@@ -1097,6 +1168,9 @@ static __init int pt_init(void)
pt_pmu.itrace.free_buffer = pt_buffer_itrace_free;
pt_pmu.itrace.sample_trace = pt_trace_sampler_trace;
pt_pmu.itrace.sample_output = pt_trace_sampler_output;
+ pt_pmu.itrace.core_size = pt_trace_core_size;
+ pt_pmu.itrace.core_output = pt_trace_core_output;
+ pt_pmu.itrace.coredump_config = RTIT_CTL_TSC_EN | RTIT_CTL_DISRETC;
pt_pmu.itrace.name = "intel_pt";
ret = itrace_pmu_register(&pt_pmu.itrace);

--
1.8.5.2